Manually operated working device having a speed that is adjusted automatically

ABSTRACT

The invention relates to a motor-driven operating device that comprises a guide handle ( 1 ). Two sensor elements are provided on the guide handle and in two handle areas ( 2, 3 ) for detecting the hands of an operator. An ignition device ( 7 ) of the motor is controlled by means of a security control device ( 6 ) in such a way that the speed can only be increased beyond a security speed when the guide handle ( 1 ) is held with both hands, whereby said security control device evaluates the sensor signals. The motor speed is limited to the security speed when the two sensor signals are missing.

[0001] Such an implement, such as, for example, a vibratory tamper forsoil compaction or an impact hammer, has a gasoline engine, butoccasionally also a diesel engine or an electric motor, for the drive.Provided no electric starter is provided, the engine is normally startedby actuating the pulling cable of a reversing starter. To this end, theoperator takes a firm hold of the tamper with one hand, for example,while he pulls the pulling cable with the other hand. Since the throttlelever of the engine usually has to be set to full throttle for starting,the engine runs immediately at a high speed, which is often even abovethe operating speed. As a result, a centrifugal clutch coupling theengine to the tamping system is closed, as a result of which the tampingsystem is put into operation. The result of this is that the tamperperforms pronounced tamping movements and can hardly be controlled bythe operator, who at this moment is holding the tamper only with onehand. Operation is made even more difficult owing to the fact that achoke valve normally present at the carburetor is closed duringstarting, and this choke valve has to be opened again to end thestarting operation. To this end, the operator must try to reach andactuate the choke lever, which is arranged at a different point from thepulling cable of the reversing starter.

[0002] An arrangement for controlling the speed of an internalcombustion engine in an implement which can be guided at a handle isproposed in subsequently published DE 198 34 443, in which arrangement adetecting device has a sensor system on the handle, this sensor systembeing able to automatically detect whether the implement is being guidedproperly. If it is detected that the implement is not being guidedproperly, the detecting device merely enables the engine speed to be setto a safety speed below an operating speed of the internal combustionengine. In this case, the safety speed is below an engagement speed atwhich, for example, a centrifugal clutch of a tamper engages.

[0003] The basic idea described in DE 198 34 443 is to be furtherdeveloped by the present invention. The object of the invention istherefore to specify a hand-guided implement in which dangerous workingstates due to uncontrolled engine speed increases are avoided and whichpermits easy operation.

[0004] The object is achieved according to the invention by hand-guidedimplements which are defined in the coordinated patent claims 1 and 2.Advantageous further developments of the invention can be gathered fromthe dependent claims.

[0005] In the first embodiment of the invention according to patentclaim 1, a sensor device for detecting the hands of an operator andproducing a corresponding handle signal is provided in a guide handle ofthe implement. Furthermore, a safety control is provided for evaluatingthe handle signal of the sensor device, detecting a starting operationof the engine and driving a speed-setting device, the speed settingbeing effected in accordance with the following rules: a speed increaseis permitted only up to a safety speed below the operating speed whenthe engine is started. A speed increase is permitted up to the operatingspeed after a time interval detected by the safety control has expired,i.e. the previous speed limit is neutralized. The engine speed isimmediately limited to the safety speed when the handle signal isabsent, e.g. when the operator lets go of the guide handle.

[0006] The second embodiment of the invention as claimed in patent claim2 is fundamentally based on the same principle as the first embodiment,although the sensor device at the guide handle has at least two sensorelements which are assigned in each case to a hand of the operator andwhich produce a sensor signal in each case when the associated hand isdetected. In a safety control, the sensor signals are evaluated, astarting operation of the engine is detected and a speed-setting deviceof the engine is driven, the rules which are decisive for the drivingbeing modified slightly compared with the first embodiment: a speedincrease only up to the safety speed is likewise permitted when theengine is started. A speed increase beyond the safety speed is onlypossible when both sensor signals are present, that is to say when theoperator holds the guide handle with both hands. The current speed isnot influenced when only one sensor signal is present, i.e. the speedset previously is maintained. If the engine consequently still runs atsafety speed, a speed increase to operating speed may only be effectedif the operator holds the guide handle with both hands. Otherwise, thesafety speed is maintained. However, if the engine is already atoperating speed, the latter is also maintained even if the operatorremoves one hand from the guide handle and merely guides the implementwith the other hand. The speed is limited to safety speed when bothsensor signals are absent.

[0007] A common feature of both embodiments of the invention is that theholding of the guide handle by the hands of the operator isautomatically detected without the operator himself having to becomeactive, e.g. by actuating an additional safety or dead man's handle. Hemerely has to grasp the guide handle in the normal manner. The enginespeed is influenced as a function of the automatically detected holdingstates without the operator having to actuate the throttle lever of theengine.

[0008] Pressure-sensitive, optical, capacitive or ultrasonic sensors aresuitable as sensor elements.

[0009] In an especially advantageous further development of theinvention, the engine can be cut out by the safety control if apredetermined time interval which can be detected by a cut-out timingelement has expired. The cut-out timing element is triggered when bothsensor signals are absent. In practice, this means that the implementcuts off itself if the operator does not have his hands on the guidehandle during the predetermined time interval. Therefore the operatordoes not have to see to it that the implement cuts out, and unnecessaryand environmentally harmful idling of the implement is avoided.

[0010] In a further advantageous refinement of the invention, thespeed-setting device is an ignition device of the engine, this ignitiondevice having at least two characteristic maps. In this case, a firstcharacteristic map is provided for the normal operation of the engine,in which the engine speed corresponds to a position of a throttle lever.This also applies in the second characteristic map within a lower speedrange, although the engine speed is limited to the safety speed.Exceeding the safety speed is ruled out. The safety control then drivesthe ignition device by changing over between the two characteristicmaps.

[0011] These and further advantages and features of the invention areexplained in more detail below with reference to an example and with theaid of the attached figures. In the drawing:

[0012]FIG. 1 schematically shows the construction of the circuitaccording to the invention in an implement according to the secondembodiment of the invention; and

[0013]FIG. 2 shows a flow chart with the rules of the safety control forthe second embodiment of the invention.

[0014] The abovementioned first embodiment of the invention constitutesa technically simpler variant. It will be described later on by means ofa comparison with the second embodiment. Therefore the second embodimentof the invention will be described first of all with reference to theschematic representation in FIG. 1, taking a vibratory tamper for soilcompaction as an example.

[0015] The tamper (not shown) is held and guided by the operator withboth hands on a, for example stirrup-shaped, guide handle 1. The guidehandle 1 is divided into a left handle region 2 for the left hand and aright handle region 3 for the right hand. Provided in the two handleregions 2, 3 is in each case at least one sensor element which detectsthe presence of the associated hand. Suitable sensor elements are inparticular pressure-sensitive and optical sensors, capacitive orultrasonic sensors also being possible. A pressure-sensitive sensordetects the hand of the operator when it at least rests on the guidehandle 1. By a suitable arrangement, e.g. also of a plurality ofsensors, it is possible to reliably detect a situation in which the handnot only rests on the guide handle 1 but also grasps it with some forceand thus reliably holds it.

[0016] In contrast, optical sensors, e.g. photocells or otherlight-sensitive elements, may also be used in such a way that anapproach of the hand of the operator is already detected. This may bemore expedient for certain intended uses.

[0017] Each of the sensors produces a sensor signal which is directedvia lines 4, 5 to a safety control 6.

[0018] Depending on the application or implement, more than two sensorelements may also be provided, if need be in more than two handleregions or zones of the guide handle 1. The number of sensor elements tobe expediently used also depends on whether the sensor elements act moreover an area (pressure-sensitive sensors) or in a spot-like manner(photocells).

[0019] The safety control 6 evaluates the sensor signals of the sensorelements. In addition, it is able to detect the starting operation ofthe engine. To this end, an additional sensor (not shown in FIG. 1) maybe provided, this sensor detecting a speed increase of the engine fromzero. Alternatively, an ignition device 7 of the engine can also bemonitored, this ignition device 7 enabling the engine speed to beinferred on the basis of the ignition points. The provision of energy inthe ignition device 7 is also an indication that the engine has beenstarted.

[0020] The safety control 6 controls the ignition device 7, serving asspeed-setting device, in accordance with predetermined rules, which areexplained in more detail further below.

[0021] In the example described, the ignition device 7 is a generallyknown magneto high-tension capacitor ignition which is staticallyfastened to the engine housing and is excited by a two-pole magnet 8integrally cast in the fan impeller (not shown) of the engine. From theenergy obtained as a result and from the information on the cycle of theengine, the ignition device 7 determines the ignition point of theengine, which is filed in a characteristic map which establishes theoptimum ignition angle for each load of the engine, and produces anignition spark at a spark plug 9. If the optimum engine speed isexceeded, the ignition device 7 displaces the ignition point inaccordance with the characteristic map, as a result of which a furtherspeed increase does not occur. If the engine speed still increasesfurther, e.g. on account of a decreasing load, the ignition device 7additionally blanks out ignition impulses for retarded setting until theengine is again working within the desired speed range.

[0022] In the tamper according to the invention, a second controlcharacteristic map is filed in addition to the normal ignition-anglecharacteristic map, this second control characteristic map beingactivated upon appropriate triggering by the safety control 6 via acontrol line 10 and limiting the engine to a speed below the operatingspeed by advancing the end of control. This speed limiting is effectedindependently of the position of a throttle lever, with which theoperator can influence the speed in a conventional manner.

[0023] As already described in connection with the prior art, thevibratory tamper is usually equipped with a centrifugal clutch, whichrequires a certain engagement speed in order to engage it. The normaloperating speed of typically 4500 rev/min for operating the tamper liesabove the engagement speed, whereas an idling speed (e.g. 3000 rev/min)lies below the engagement speed. The idling speed is designated assafety speed, since no tamping movement possibly putting the operator orother persons at risk is effected, and the implement is thus at rest ifthe idling engine is ignored.

[0024] The energy produced in the ignition device 7 by the magneticexcitation is sufficient in order to also supply the safety control 6with energy as soon as the engine is running. For this purpose, anenergy line 11 is provided from the ignition device 7 to the safetycontrol 6.

[0025] Whereas in the embodiment of the invention described the speedlimiting by the safety control 6 is effected by changing over thecharacteristic maps filed in the ignition device 7, it is possible in avariant of the invention to carry out the speed limiting by means of aservo which is coupled to the throttle lever. In another variant of theinvention, the position of the choke in the carburetor can be varied forinfluencing the speed.

[0026] The safety control 6 is able to cut out the ignition device 7 viaa cut-off line 12, so that the engine stops immediately. This may beexpedient, for example, when the safety control 6 detects for aprolonged period (e.g. 10 s) that no hand is resting on the guide handle1.

[0027] The functioning of the tamper and the rules for the speed controlare described below with reference to the flow chart shown in FIG. 2.

[0028] During starting (step S1), the operator holds the tamper with onehand at the guide handle 1, while with the free hand he actuates areversing starter (not shown in FIG. 1) until the tamper is running.

[0029] The safety control recognizes the starting operation at theinstant t=0 (step S2) and changes over the ignition device to the secondcharacteristic map with reduced speed (step S3), so that speed limitingto the safety speed is effected. Run-up of the engine and thusengagement of the centrifugal clutch are therefore prevented.

[0030] If it is discovered in step S4 that the engine has not started orhas been cut off again, the program flow stops. If, on the other hand,the engine is running at safety speed, it is checked in step S5 whethera predetermined time interval (tmax) has expired. To this end, the timeis recorded by a cut-out timing element triggered in step S2. If thepredetermined time interval tmax is exceeded, the tamper is cut off.

[0031] Otherwise, in step S6, it is checked with reference to the sensorsignals whether the guide handle I is grasped with both hands. If thisis not the case, the engine remains at safety speed (step S3) and thechecking of the expired time—without further operation at the guidehandle 1 having been effected—takes place again in step S5.

[0032] When the two handle halves 2, 3 of the guide handle 1 aregrasped, the safety control 6 changes over in step S6 to the standardcharacteristic map (step S7), so that the engine runs up to theoperating speed predetermined by the throttle lever. As a result, thecentrifugal clutch is closed and the tamping system works as desired bythe operator. Since the operator is holding the tamper with both handsat this instant, safe guidance is ensured.

[0033] The cut-out timing element is triggered again in step S8, so thatthe time interval to be measured begins again.

[0034] An inquiry as to whether the tamper has been cut off is effectedin step S9. In step S10, the sensor signals of the sensor elements areinterrogated and evaluated, so that it can be determined whether theguide handle 1 is still held by both hands. If this is case, the programloop continues with step S7 with unaltered engine speed. The cut-outtiming element is triggered again in step S8.

[0035] If no two-handed guidance is established in step S10, it ischecked in step S11 whether guidance is single-handed if only one sensorsignal is present. If this is the case, this has no effect on the enginespeed (step S7). The cut-out timing element is then also triggered timeand time again in step S8.

[0036] When both handle halves are let go of, that is to say when thereis not even guidance with one hand, the program branches from step S11to step S12, where the cut-out timing element is triggered again andafter that a changeover to the second characteristic map is effected instep S3, as a result of which the engine speed drops by adjusting theignition point and omitting the ignition impulses until the safety speedlying below the engagement speed of the centrifugal clutch is reached.An immediate interruption in the mechanical connection between driveengine shaft and tamping system is the result.

[0037] If the operator now grasps the guide handle 1 with only one hand,the engine speed does not change on account of the decision in step S6.The control characteristic map remains active on account of step S3, andthe tamper waits with running engine, but without mechanical activity ofthe tamping system.

[0038] It is not until two-handed grasping of both handle halves 2, 3 isdetected in step S6 that the tamper starts to work again immediately.

[0039] If, on the other hand, the tamper is not started up during thetime interval tmax by grasping both handle halves 2, 3, the controldevice detects a work pause and automatically cuts off the tamper.

[0040] It is pointed out that, although the above embodiment has beendescribed taking a gasoline engine as an example, the construction basedon the invention and the associated rules may also be used in otherengines such as diesel engines and electric motors.

[0041] In the first embodiment of the invention referred to above, onlyone sensor is provided for the entire guide handle 1, this sensorproducing a sensor signal, serving as handle signal, when at least onehand touches or grasps the guide handle 1. A differentiation as towhether the operator is holding the handle with one hand or with bothhands therefore does not take place in the first embodiment.

[0042] When the engine is started, a speed increase is permitted only upto the safety speed, as in the second embodiment. At the same time, atiming element is triggered. After a time interval (e.g. 5 s)predetermined by the timing element has expired and the handle signal ispresent, the safety control permits a speed increase beyond the safetyspeed. If the handle signal is no longer present, the engine speed isimmediately limited again to the safety speed. Running-up of the engineis therefore only possible if at least one hand is resting on the guidehandle 1.

[0043] Even if the first embodiment of the invention therefore does nothave the same convenient functionality as the second embodiment, thefeatures relevant to safety are realized.

[0044] The invention can be very advantageously used not only in thevibratory tamper described but also in other engine-operated implements,such as vibratory plates, vibratory rollers, hammers and power saws.

1. A hand-guided implement having an engine; a speed-setting device (7)for the engine for setting at least one operating speed and a safetyspeed below the operating speed; at least one guide handle (1) with asensor device for detecting the hands of an operator on the guide handleand producing a corresponding handle signal; and having a safety control(6) for evaluating the handle signal of the sensor device, detecting astarting operation of the engine and driving the speed-setting device inaccordance with the following rules: speed increase only up to thesafety speed when the engine is started; triggering of a timing element;permitting a speed increase beyond the safety speed when a time intervalpredetermined by the timing element has expired and the handle signal ispresent; limiting the speed to the safety speed when the handle signalis absent.
 2. A hand-guided implement having an engine; a speed-settingdevice (7) for the engine for setting at least one operating speed and asafety speed below the operating speed; at least one guide handle (1)with a sensor device for detecting the hands of an operator on the guidehandle; the sensor device having at least two sensor elements which canbe assigned in each case to a hand of the operator at the guide handleand which accordingly produce a sensor signal in each case when the handis detected; the sensor signals being directed to a safety control (6),and the safety control (6) being designed for evaluating the sensorsignals of the sensor elements, detecting a starting operation of theengine and driving a speed-setting device in accordance with thefollowing rules: speed increase only up to the safety speed when theengine is started; permitting a speed increase beyond the safety speedwhen both sensor signals are present; no influencing of the currentspeed when only one sensor signal is present; limiting the speed to thesafety speed when both sensor signals are absent.
 3. The implement asclaimed in claim 2, characterized in that one of the sensor elements isarranged in a left handle region (2) of the guide handle for the lefthand of the operator and the other sensor element is arranged in a righthandle region (3) for the right hand.
 4. The implement as claimed in oneof claims 1 to 3, characterized in that the sensor device has at leastone pressure-sensitive, optical, capacitive or ultrasonic sensor.
 5. Theimplement as claimed in one of claims 1 to 4, characterized in that theengine can be cut out by the safety control (6); a cut-out timingelement belonging to the safety control (6) can be triggered when bothsensor signals are absent; and in that the safety control (6) cuts outthe engine when a predetermined time interval which can be detected bythe cut-out timing element has expired.
 6. The implement as claimed inone of claims 1 to 5, characterized in that the speed-setting device isan ignition device (7) of the engine.
 7. The implement as claimed inclaim 6, characterized in that the ignition device (7) has at least twocharacteristic maps, namely a first characteristic map, according towhich the engine speed corresponds to a position of a throttle lever,and a second characteristic map, according to which the engine speedcorresponds to a position of the throttle lever but is limited to thesafety speed, and in that the safety control (6) drives the ignitiondevice by changing over between the two characteristic maps.
 8. Theimplement as claimed in claim 6, characterized in that the ignitiondevice (7) in each case has a characteristic map for the operating speedand for the safety speed.
 9. The implement as claimed in one of claims 1to 8, characterized in that the safety control (6) is supplied withenergy from the speed-setting device.
 10. The implement as claimed inone of claims 1 to 9, characterized in that a further sensor is providedfor determining the starting operation of the engine.